In a large bowl, combine pretzels, Cheerios, Chex, peanuts, Smarties; set aside.
In medium microwave-safe bowl, combine white chocolate baking pieces and shortening. Microwave on 100% power (high) for 1 to 2 minutes or until baking pieces are melted, stirring every minute until smooth. Pour over cereal mixture; toss gently to coat.
Spread on large piece of waxed paper to cool. Break apart large clusters. Store in airtight container at room temperature for up to 1 week.